SOLAR-WIND STREAM INTERFACES IN COROTATING INTERACTION REGIONS - SWICS ULYSSES RESULTS/

Motivated by the well-known differences in charge state and even eleme ntal composition of the slow solar wind as compared to high-speed stre ams, we have analyzed observations made by the Solar Wind Ion Composit ion Spectrometer (SWICS)/Ulysses mass spectrometer of the series of co rotating interaction regions (CIRs) encountered by Ulysses in 1992/199 3 at 4.5-5.4 AU from the Sun. Stream interfaces (SIs) are first identi fied within each CIR using the kinetic parameters (density and thermal speed) of the main components, protons and alpha particles. We then s how that SIs are also the location of the expected compositional chang es in the heavy ion components, such as the freezing-in temperatures o f C and O and the strength of FIP fractionation as given by the Mg/O a bundance ratio, to within the time resolution with which these paramet ers may be obtained by SWIGS. The changes in freezing-in temperatures are so clear that they in turn may be used as a robust indicator of th e SI location and even reveal that some of the SI crossings were in fa ct multiple. We conclude that the heavy ion composition of the solar w ind changes abruptly at the SI and remains well preserved out to large heliocentric distances.